Influence of Severity and Types of Astigmatism on Visual Acuity in School-Aged Children in Southern China
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Int J Ophthalmol, Vol. 11, No. 8, Aug.18, 2018 www.ijo.cn Tel:8629-82245172 8629-82210956 Email:[email protected] ·Investigation· Influence of severity and types of astigmatism on visual acuity in school-aged children in southern China Li-Li Wang, Wei Wang, Xiao-Tong Han, Ming-Guang He Zhongshan Ophthalmic Center, State Key Laboratory of DOI:10.18240/ijo.2018.08.20 Ophthalmology, Sun Yat-Sen University, Guangzhou 510060, Guangdong Province, China Citation: Wang LL, Wang W, Han XT, He MG. Influence of severity Correspondence to: Ming-Guang He. State Key Laboratory and types of astigmatism on visual acuity in school-aged children in of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen southern China. Int J Ophthalmol 2018;11(8):1377-1383 University, 54S. Xianlie Road, Guangzhou 510060, Guangdong Province, China. [email protected] INTRODUCTION Received: 2018-04-26 Accepted: 2018-05-28 stigmatism is one of the most common refractive A errors. Severe astigmatism without effective correction Abstract leads to visual impairment, amblyopia, and myopia during ● AIM: To investigate the influence of astigmatism on visual emmetropization[1-3]. Visual impairment due to astigmatism acuity in school-aged children, and to define a cutoff for may also cause insufficient educational performance and affect clinically significant astigmatism. working potential[4-6]. The prevalence of astigmatism in Chinese ● METHODS: This is a population-based, cross-sectional children ranges from 2% to 42.7%[7-11]. Previous studies also study. Among 5053 enumerated children aged 5-15y have documented that children of Hispanic and African- in Guangzhou, 3729 (73.8%) children aged 7-15 with American ethnicities had higher risk of astigmatism than non- successful cycloplegic auto-refraction (1% cyclopentolate) Hispanic white children[12]. Asian ethnicity was also related and a reliable visual acuity measurement were included. with higher risk of astigmatism[13-14]. However, these findings Ocular measurement included external eye, anterior are considerably different and not directly comparable due to segment, media and fundus and cycloplegic auto-refraction. the differences in disease definition. Primary outcome measures included the relationship Knowledge of the influence of severity and subtypes of between severity and subtypes of astigmatism and the astigmatism on visual performance is essential for a better prevalence of visual impairment. Three criteria for visual understanding of the impact of astigmatism on visual function impairment were adopted: best-corrected visual acuity and probably amblyopia. It is well established that astigmatism (BCVA) ≤0.7, uncorrected visual acuity (UCVA) ≤0.5 or <0.7 lead to visual reduction for both distant and near distance. in the right eye. However, the cutoff of clinical significant astigmatism has ● RESULTS: Increases of cylinder power was significantly not been established currently. For example, the definition associated with worse visual acuity (UCVA: β=0.051, of astigmatism varied across population-based studies. P<0.01; BCVA: β=0.025, P<0.001). A substantial increase Hashemi et al[15] used the cylinder of 0.5 D as the cutoff in the in UCVI and BCVI was seen with astigmatism of 1.00 population survey in Iran. The Sydney Myopia Study (SMS) diopter (D) or more. Astigmatism ≥1.00 D had a greater BCVI and Collaborative Longitudinal Evaluation of Ethnicity and prevalence than cylinder power less than 1.00 D (OR=4.20, Refractive Error Study (CLEERS) adopted a cylinder of 1.0 D 95%CI: 3.08-5.74), and this was also true for hyperopic, as the cutoff for astigmatism definition[12,16-17]. The Baltimore emmetropic and myopic refraction categories. Oblique Pediatric Eye Disease Study (BPEDS), Strabismus, Amblyopia astigmatism was associated with a higher risk of BCVI and Refractive Error in Singaporean Children Study (STARS) relative to with the rule astigmatism in myopic refractive and Multi-Ethnic Pediatric Eye Disease Study (MEPEDS) category (OR=12.87, 95%CI: 2.20-75.38). used a relatively high cutoff (cylinder ≥1.50 D) to examine the ● CONCLUSION: Both magnitude and subtypes of prevalence of astigmatism in preschool children[13,18-20]. astigmatism influence the prevalence of visual impairment The Refractive Error Study in Children (RESC) is a multi- in school children. Cylinder ≥1.00 D may be useful as a country large-scale population-based, cross-sectional survey cutoff for clinically significant astigmatism. of refractive error and visual impairment in school-aged ● KEYWORDS: astigmatism; visual acuity; children; children, which has used standard methodology and common population-based study definition[7,21]. Using Guangzhou RESC data, we found that 1377 Impact of astigmatism on visual acuity the overall prevalence of astigmatism (cylinder≥0.75 D) was as a minimum meridian refraction from -0.5 D to +0.75 D. 42.7% in Chinese children[7]. The objective of this study was Spherical degree was defined as the angle of the minimum to further explore the association of astigmatism with visual meridian power. Cylindrical refractive error was expressed in impairment and to identify the cutoff of astigmatism for negative cylinder form. Types of astigmatism were defined functional visual impairment. based on the minus astigmatism axis of the right eye: with SUBJECTS AND METHODS the rule (WTR; cylinder axis 0° to 30° or 150° to 180°), Study Population The RESC surveys were conducted using against the rule (ATR; cylinder axis 60° to 120°) and oblique a standardized protocol with randomized cluster sampling of (OBL; cylinder axis 31° to 59° or 121° to 149°). The visual the targeted study population, which was detailed in previous impairment was defined based on UCVA and on BCVA. Three [7,21-22] reports . The RESC survey was reviewed and approved cut-offs were used for visual impairment: UCVA≤20/40 (0.5) by human experimentation committees or Institutional Review or UCVA≤20/32 (0.7) or BCVA≤20/32 (0.7). Boards (IRB) of World Health Organization. Approval for Statistical Analysis Statistical analysis was performed using the studies at specific sites was obtained from local health Stata Version 11.0 (Stata Corporation, College Station, Texas, authorities. Written informed consent for each examined child USA). The data on the right eyes was used for analysis. The was obtained from a parent or other responsible adult during prevalence of astigmatism was categorized into 10 subgroups the household enumeration. The research followed the tenets based on cylinder severity: 0 D, 0.25 D, 0.50 D, 0.75 D, 1.00 D, of the Declaration of Helsinki. 1.25 D, 1.50 D, 1.75-2.00 D, 2.25-3.00 D and >3.00 D. Multi- Ocular Examinations Clinical examination of participants variate logistic regression analysis was used to explore the including external eye, anterior segment, media and association of visual impairment and astigmatism severity fundus were performed by trained RESC optometrists after controlling for age, sex, and spherical error. Confidence or ophthalmologist using standardized protocols. Ocular intervals (CI) and P values (significant at the <0.05 level) for alignment was assessed using the cover and uncover test at prevalence estimates and regression models were calculated near (0.5 m) and distance (4 m). Hirschberg corneal light reflex with adjustment for cluster effects associated with the sampling was used to measure the degree of tropia. design. Wald binomial confidence intervals for odds ratios Visual Acuity and Cycloplegic Refraction Uncorrected (OR) were calculated. Multivariate linear regression analysis monocular distance visual acuity was measured at 4 m with a was performed to investigate the association of astigmatism retro-illuminated logMAR chart (Precision Vision, La Salle, and logMAR visual acuity. A P-value less than 0.05 was IL, USA), in a monocular fashion with the right eye followed considered statistically significant. by the left eye, using five tumbling “E” optotypes on each line RESULTS and recorded as the smallest line read with one or no errors. If Study Population A total of 5053 children age 5-15y were uncorrected visual acuity (UCVA) in either eye was 20/40 (0.5) enumerated in Guangzhou, of whom 4364 (86.4%) children or worse, best-corrected visual acuity (BCVA) was measured were examined. Among of them 4312 (85.3%) children after cycloplegic refraction. Autorefraction was performed after cycloplegia. Cycloplegia received successful cycloplegic auto-refraction (1% was induced with two drops of 1% cyclopentolate administered cyclopentolate) and a reliable visual acuity measurement. After to each eye 5min apart and a third drop administered if a excluding 51 children with visual impairment due to non- pupillary light reflex was still present after 20min. Successful refractory causes (amblyopia, cataract, retinal disorder and cycloplegia and pupil dilation were evaluated after an other causes), 4261 children underwent further evaluation. additional 15min and was defined as a pupil dilution of more Visual acuity testing is challenging in children age 5-6y than 6 mm and without light reflex. Refractive error was because visual and cognitive function is still developing. determined by cycloplegic streak retinoscopy followed by After excluding 532 (12.49%) children age 5-6y, a total of measurement with a handheld auto-refractor (Retinomax 3729 children age 7-15y were included in the current analysis K-plus, Nikon, Tokyo, Japan) after visual acuity measurement. finally. For the current paper, auto-refraction data with complete Association of Astigmatism and Visual Impairment Figure 1 cycloplegia were used. shows the distribution of logMAR BCVA and UCVA stratified Definitions of Refractive Error and Visual Impairment by astigmatism severity of hyperopic, emmetropic and myopic Minimum meridian is the meridian with the smallest refractive spherical categories. As expected, BCVA and UCVA decreased error, the one closest to 0.0 D. Absolute minimum meridian is with a higher degree of cylinder. UCVA was more affected the absolute value of minimum meridian. Myopia was defined by astigmatism and sphere than BCVA.